Add error recovery for statements and if-conditions

grammar.coffee

@@ -1,5 +1,5 @@
 compiler = require("tree-sitter-compiler")
-{ choice, repeat, seq, sym, keyword, token, optional, prec } = compiler.rules
+{ choice, err, repeat, seq, sym, keyword, token, optional, prec } = compiler.rules
 
 commaSep1 = (rule) ->
   seq(rule, repeat(seq(",", rule)))
@@ -32,11 +32,11 @@ module.exports = compiler.grammar
       @var_declaration)
 
     expression_statement: -> seq(
-      @expression, terminator())
+      err(@expression), terminator())
 
     if_statement: -> seq(
       keyword("if"),
-      "(", @expression, ")",
+      "(", err(@expression), ")",
       @statement)
 
     switch_statement: -> seq(

grammar_test/errors.txt

@@ -0,0 +1,36 @@
+============================================
+Bad statements
+============================================
+
+what the heck is this
+y();
+
+if (x) {
+  >>>
+  var y = right
+}
+
+---
+
+(program
+  (expression_statement (ERROR 't'))
+  (expression_statement (function_call (identifier)))
+  (if_statement (identifier) (statement_block
+    (expression_statement (ERROR '>'))
+    (var_declaration (var_assignment (identifier) (identifier))))))
+
+============================================
+Bad if conditions
+============================================
+
+if (%$&^)
+  wat();
+
+okWhatever();
+
+---
+
+(program
+  (if_statement (ERROR '%')
+    (expression_statement (function_call (identifier))))
+  (expression_statement (function_call (identifier))))